The endogenous cholinergic neurotransmitter, acetylcholine, exerts its biological effect via two types of cholinergic receptors, the muscarinic Acetyl Choline Receptors (mAChR) and the nicotinic Acetyl Choline Receptors (nAChR).
Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand gated ion channels and widely distributed throughout the central (CNS) and peripheral (PNS) nervous systems. At least 12 subunit proteins, i.e. α2-α10 and β2-β4, have been identified in neuronal tissue. These subunits provide for a great variety of homomeric and heteromeric combinations that account for the diverse receptor subtypes. For example, the predominant receptor that is responsible for high affinity binding of nicotine in brain tissue has composition α4β2, while another major population of receptors is comprised of the homomeric α7.
Discovery of the important role played by nAChRs in several CNS disorders has called attention to these membrane proteins and to ligands able to modulate their functions. The existence of different subtypes at multiple levels has complicated the understanding of this receptor's physiological role, but at the same time has increased the efforts to discover selective compounds in order to improve the pharmacological characterization of this kind of receptor and to make safer the possible therapeutic use of its modulators.
WO 2004/029053, WO 2007/138037, WO 2007/138038 and WO 2009/150138 all describe oxadiazolyl-diazabicyclononane derivatives, which are found to be cholinergic ligands at the nicotinic acetylcholine receptors and modulators of the monoamine receptors and transporters. However, the labelled pyrrolyl-oxadiazole-diazabicyclononane derivatives of the present invention are not reported.